This invention relates to a magnetic recording medium, more specifically to a magnetic recording medium excellent in electromagnetic transducing properties.
In the prior art, recording magnetic media such as a magnetic tape have been prepared by coating a magnetic coating comprising a ferromagnetic powder, a binder resin, a solvent and others on a non-magnetic support surface and drying the coated support.
However, in this kind of a magnetic recording medium, while the magnetic layer thus formed on the non-magnetic support is a single layer, it is necessary to cover a wide frequency band region from a low region to a high region by one kind of a magnetic powder.
Particularly, in the tendency of high density recording in recent years, it has been demanded to improve recording properties at a high region and also to lower noises so that a magnetic powder having high Hc and high BET values has been employed.
However, in a magnetic layer comprising a single layer, there involves the problem that frequency characteristics at a low region become insufficient.
For solving such a problem, in a magnetic recording medium such as a magnetic recording medium for video, there has been proposed magnetic recording media having plural magnetic layers in order to heighten a magnetic recording capacity, or to improve magnetic recording properties both at a high frequency region and at a low frequency region of a magnetic recording medium whereby balancing frequency characteristics at a low region and at a high region (see Japanese Unexamined Patent Publications No. 98803/1973 and No. 172142/1984, Japanese Patent Publication No. 2218/1957, Japanese Unexamined Patent Publications No. 56228/1976 and No. 146211/1988).
According to these known techniques, a magnetic recording medium is so designed that an upper layer and a lower layer of a magnetic layer have different functions, and that video output is conducted in the upper layer and chroma and audio outputs are conducted in the lower layer.
However, in such a conventional magnetic recording medium having magnetic layers with different functions, a surface roughness degree of a non-magnetic support exerts great influence on a magnetic layer, whereby electromagnetic transducing properties of magnetic layers having different properties are worsened.
For improving properties at a frequency region, particularly at a low frequency region, there is a technique in which ferromagnetic powder having a large particle size is added to a magnetic layer. However, in this technique, there involves the problem that dispersibility of a ferromagnetic powder is worsened and also dropping-out of a powder (drop out) is liable to occur.